Mechanical refrigeration systems, and related heat transfer devices such as heat pumps and air conditioners, using refrigerant liquids are well known in the art for industrial, commercial, and domestic uses. Several fluorocarbon-based fluids have found widespread use in many residential, commercial and industrial applications, including as the working fluid in systems such as air conditioning, heat pump and refrigeration systems. Because of certain suspected environmental problems, including the relatively high global warming potentials associated with the use of some hydrofluorocarbon (“HFC”) based compositions that have heretofore been used in these applications, it has become increasingly desirable to use fluids having low global warming potentials (“GWP”) in addition to low or zero ozone depletion potentials, such as hydrofluoroolefins (hereinafter “HFOs”). For example, a number of governments have signed the Kyoto Protocol to protect the global environment and setting forth a reduction of CO2 emissions (global warming). Thus, there is a need for alternatives to replace high global warming HFCs.
One important type of refrigeration system is known as a “low temperature refrigeration system.” Such systems are particularly important to the food manufacture, distribution and retail industries in that they play a vital role in ensuring that food which reaches the consumer is both fresh and fit to eat. In such low temperature refrigeration systems, a commonly used refrigerant has been HFC-404A or R-404A (the combination of HFC-125:HFC-143a:HFC134a in an approximate 44:52:4 weight percent). R-404A has an estimated GWP of 3922.
It is generally considered important, however, with respect to heat transfer fluids, that any potential substitute must also possess those properties present in many of the most widely used HFC based fluids, such as excellent heat transfer properties, chemical stability, low- or no-toxicity, non-flammability, and lubricant compatibility, among others. In addition, any replacement or retrofit for R-404A would desirably be a good match for the operating conditions of R-404A in such systems order to avoid modification or redesign of the system.
With regard to efficiency in use, it is important to note that a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy. In other words, a proposed new refrigerant that has an improved GWP and/or ODP relative to an existing fluid might nevertheless be less environmentally friendly than the fluid it is replacing if another characteristic of the proposed new fluid, such as efficiency in use, results in increased environmental emissions indirectly, such as by requiring higher fuel combustion to achieve the same level of refrigeration. It is thus seen that the selection of a replacement or retrofit fluid is a complicated, challenging endeavor that may not have predictable results.
Furthermore, it is generally considered desirable for HFC refrigerant substitutes to be effective without major engineering changes to conventional vapor compression technology currently used with HFC refrigerants.
Flammability is another important property for many applications. That is, it is considered either important or essential in some applications, including particularly in certain heat transfer applications, to use compositions that are non-flammable. One advantage of the use of non-flammable refrigerants in a heat transfer system is flame suppression equipment will not be required in such systems in order to mitigate possible risks associated with leakage of refrigerant from the system. This advantage is especially important in systems that would suffer from the secondary disadvantage of the increased system weight that would be associated with, for example, transport refrigeration systems.
As used herein, the term “non-flammable” refers to compounds or compositions which are determined to be non-flammable as determined in accordance with ASTM standard E-681-2009 Standard Test Method for Concentration Limits of Flammability of Chemicals (Vapors and Gases) at conditions described in ASHRAE Standard 34-2016 Designation and Safety Classification of Refrigerants and described in Appendix B1 to ASHRAE Standard 34-2016, which is incorporated herein by reference and referred to herein for convenience as “Non-Flammability Test”. Unfortunately, many materials that might otherwise be desirable for use in refrigerant compositions are not non-flammable as that term is used herein. For example, fluoroalkane difluoroethane (HFC-152a) and fluoroalkene 1,1,1-trifluoropropene (HFO-1243zf) have flammability profiles which make them less preferred for use in some applications.
It is critical for maintenance of system efficiency and proper and reliable functioning of the compressor, that lubricant circulating in a vapor compression heat transfer system is returned to the compressor to perform its intended lubricating function. Otherwise, lubricant might accumulate and become lodged in the coils and piping of the system, including in the heat transfer components. Furthermore, when lubricant accumulates on the inner surfaces of the evaporator, it lowers the heat exchange efficiency of the evaporator, and thereby reduces the efficiency of the system. For these reasons, it is desirable for many systems that the refrigerant is miscible over at least the operating temperature range of the system with the lubricant that is used in the system.
Since R-404A is currently commonly used with polyol ester (POE) lubricating oils, a proposed R-404A replacement refrigerant is desirably miscible with POE lubricants over the temperature range in the system and for the concentrations of lubricant that are present in the system, particularly over the operating temperature ranges in the condenser and evaporator.
Since R-22 is currently commonly used with mineral oil (MO), alkyl benzene (AB) and polyol ester (POE) lubricating oils, a proposed R-22 replacement refrigerant is desirably miscible with each of MO, AB and POE lubricants over the temperature range in the system and for the concentrations of lubricant that are present in the system, particularly over the operating temperature ranges in the condenser and evaporator.
Applicants have thus come to appreciate a need for compositions, and particularly heat transfer compositions, that are highly advantageous in heating and cooling systems and methods, particularly medium and low temperature refrigeration systems, and even more particularly medium and low temperature refrigeration systems, including medium and low temperature transport refrigeration systems, that have been designed for use with or are suitable for use with R-404A and/or R-22.